1. Field of the invention
The present invention relates to a control system for an internal combustion engine of a vehicle with an automatic transmission, more specifically to an output control of the engine in connection with a shift operation in the automatic transmission.
2. Description of the prior art
In a vehicle provided with an automatic transmission, there have been various proposals for reducing a torque shock or jolt through a shift operation from one gear stage to another in the automatic transmission. In a control system disclosed in U.S. Pat. No. 4,226,447, an ignition timing of the engine is controlled in accordance with a vehicle speed as a shift operation occurs so that an engine output power or torque is changed to reduce the torque shock due to the shift operation. U.S. Pat. Nos. 4,355,550, 4,370,903 and 4,403,527 disclose similar control systems.
In controlling the engine output during the shift operation, it should be noted that a time period from a generation of a control signal for the shift operation to a completion of the shift operation varies depending on a vehicle operating condition such as engine speed, an engine load defined by such as a throttle opening, intake gas amount and the like, line hydraulic pressure in the transmission, gear stages involved in the shift operation and the like.
In view of this, the conventional ignition timing output control is adapted to be initiated to control the engine output torque after a predetermined time period from the generation of the control signal for the shift operation.
It should however be noted that the engine speed may drop unduly in the case where a braking operation occurs before the shift operation is completed, since the engine output torque is controlled to be reduced during the shift operation. This may result in a deterioration of controllability of the vehicle.